Question

An astronomical telescope has an angular magnification of magnitude $5$ for distant objects. The separation between the objective and the eye-piece is $36 \,cm$ and the final image is formed at infinity. The focal length ${{f}_{o}}$ of the objective and ${{f}_{e}}$ of the eye-piece are respectively

• A. 45 cm and 9 cm
• B. 50 cm and 10 cm
• C. 7.2 cm and 5 cm
• D. 30 cm and 6 cm

Answer 1

Answer: (D)

30 cm and 6 cm

Answer 2

$\frac{{{f}_{o}}}{{{f}_{e}}}=5$
${{f}_{o}}=5{{f}_{e}}$
${{f}_{o}}+{{f}_{e}}=36$
$5{{f}_{e}}=6\,cm$ and ${{f}_{e}}=30\,cm$